Transmitter optical module implemented with thermo-electric controller

ABSTRACT

A transmitter optical module is disclosed. The optical module includes a plurality of LDs each emitting light with specific wavelengths different from others, a TEC including a post in bottom plate thereof through which currents to driver the TEC is supplied, and a body portion including an electrical plug made of multi-layered ceramics. The multi-layered ceramic in a lowermost ceramic layer thereof provides electrical pads to supply current to the TEC through the post. The post and the pads are configured in side-by-side arrangement such that the post in the TEC is put between two pads in the lowermost ceramic layer.

BACKGROUND

1. Field

The present application relates to a transmitter optical module thatinstalls a thermo-electric controller (hereafter denoted as TEC)therein.

2. Description of the Related Art

A transmitter optical module has been used as an optical signal sourcefor the optical communication system, and/or a pumping source for anoptical fiber amplifier. The transmitter optical module installs thereina semiconductor laser diode (hereafter denoted as LD) to convert anelectrical signal into an optical signal. Because an emission wavelengthof the LD strongly depends on an operating temperature of the LD, thetransmitter optical module is often implemented with a TEC to keep atemperature of an LD constant. The U.S. Pat. No. 6,821,030, U.S. Pat.No. 7,106,978, and U.S. Pat. No. 8,213,472, have been disclosed such antransmitter optical module installing a TEC therein.

The present application is to provide an improved arrangement to supplycurrent to a TEC installed within the transmitter optical module.

SUMMARY

A transmitter optical module according to one of embodiments comprises aplurality of LDs, a TEC, and a body portion enclosing the LDs and theTEC therein. The TEC includes a bottom plate on which posts to supplycurrent to the TEC is provided. The body portion includes an electricalplug made of multi-layered ceramics. The multi-layered ceramics providespads through which the current to drive the TEC is supplied. A featureof the transmitter optical module is that the pads in the multi-layeredceramics and the posts in the bottom plate of the TEC are arranged inside-by-side such that the pads put the posts therebetween; and areconnected to the posts via bonding wires.

One of embodiments includes a lowermost ceramic layer and a firstceramic layer provided on the lowermost ceramic layer. The pads areformed on the top surface of the lowermost ceramic layer. The firstceramic layer provides interconnections on the top surface and the backsurface thereof. The pads on the lowermost ceramic layer areelectrically connected to the interconnections formed in the backsurface of the first ceramic layer and brought to the outside of thebody portion. The bottom plate of the TEC is slipped under the lowermostceramic layer; while, the first ceramic layer exposes top surface of thelowermost ceramic layer only in both sides thereof. Thus, the padsformed in the exposed top surface of the lowermost ceramic layer putsthe posts in the bottom plate of the TEC therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments will be described withreference to the following figures:

FIG. 1 shows an outer appearance of a transmitter optical moduleaccording to an embodiment;

FIG. 2 shows an inside of the transmitter optical module illustrated inFIG. 1;

FIG. 3 shows a side cross section of the transmitter optical moduleillustrated in FIGS. 1 and 2;

FIG. 4 illustrates a TEC with a post and a lowermost ceramic layer witha pad disposed in side-by-side arrangement to the post;

FIG. 5 is a plan view showing the post, the pad and bonding wireselectrically connecting the pad to the post;

FIG. 6 magnifies a rear portion of the multi-layered ceramics providingthe pad in the top surface of the lowermost layer thereof;

FIG. 7 shows a side cross section of the TEC with the post, themulti-layered ceramics with the pad on a top surface of the lowermostlayer;

FIG. 8 shows an inside of a transmitter optical module according toanother embodiment; and

FIG. 9 shows a side cross section of the TEC, electrical elements on theTEC, and the multi-layered ceramics implemented within the transmitteroptical module shown in FIG. 8.

DETAILED DESCRIPTION

Some embodiments will be described as referring to drawings. Atransmitter optical module shown in FIGS. 1 to 3 includes a plurality ofLDs within a package, and each of LDs emits light with a specificwavelength different from others. Such a transmitter optical module isinstalled in an optical transceiver applicable to the wavelengthdivision multiplexing (WDM) system.

FIG. 1 shows an outer appearance of the transmitter optical module 10according to an embodiment. The transmitter optical module 10 shown inthe figures primarily comprises a body portion 11 and a coupling portion12. The body portion 11 has a box shape with a ceiling 13 to seal aninside thereof hermetically. A rear end of the body portion 11 providesan electrical plug to communicate with an external circuit electrically.The coupling portion 12 is assembled with one wall of the body portion11 in a side opposite to the electrical plug 14. The description belowassumes only for the explanation sake that the front side of the module10 corresponds to a side where the coupling portion 12 is provided;while, the rear is a side the electrical plug 14 is formed.

FIG. 2 is also a perspective drawing of the optical module viewed fromthe front top, where a part of the body portion 11 is removed to showthe inside thereof. FIG. 3 is a cross section along the longitudinaldirection of the body portion 11 of the optical module 10. The bodyportion 11 installs a TEC 21, the LDs 32, a driver 33, and some opticalcomponents therein. The LDs 32 and the driver 33 are mounted on the TEC21 through the first carrier 30; while, the optical components such asfirst lenses 36, monitor photodiodes (hereafter denoted as PD) 38, anoptical multiplexer 39, and the second lens 40 are mounted on the TEC 21through the second carrier 35. Further specifically, the LDs 32 aremounted on the first carrier via LD sub-mounts 31; while, the monitorPDs 38 are mounted on the second carrier 35 via a beam splitter 37. Thefirst carrier 30 also mounts a wiring substrate 34 thereon. Twocarriers, 30 and 35, are preferably made of material having good thermalconductivity, such as aluminum nitride (AlN), copper tungsten (CuW), andso on.

Each of LDs 32 emits light with a specific wavelength different fromothers. The optical multiplexer 39 multiplexes light depending on thewavelengths thereof to generate a single beam to be coupled with asingle fiber through the second lens 40. The embodiment shown in thefigures installs four (4) LDs; and the wavelengths of light emitted fromthe LDs 32 follow the LAN-WDM standard where a wavelength difference tothe next grid is defined to be around 5 nm. The body portion 11, asalready explained, has a box shape with 5 to 8 mm square. The couplingportion 12, which receives an external ferrule secured in a tip of anexternal fiber, couples the LDs in the body portion 11 optically withthe external fiber. The electrical plug 14, which extends outwardly, ismade of multi-layered ceramics; where the embodiment shown in thefigures has four ceramic layers, 15 to 17, and 44.

The first ceramic layer 15 in the electrical plug 14 includes a topsurface 18, on which electrical pads 18 b are formed, and a back surface20 where other electrical pads may be formed but not explicitlyillustrated in the figures. The electrical plug 14 is electricallyconnected to external circuits with, for instance, a flexible printedcircuit (FPC) board, and/or electrical connectors with lead terminals incontact with the pad 18 b.

The driver 33 mounted on the first carrier 30 is electrically connectedto the wiring substrate 34 and the LDs 32 with bonding wires 50. Thewiring substrate 34 provides interconnection with an arrangement of themicro-strip line and/or the coplanar line to secure the transmissionimpedance thereof. Because the driver 33, or the LDs 32, operates in aspeed reaching, or occasionally exceeding, 10 Gbps; the impedancematching of the transmission lines to that of the driver 33 and the LDs32 are one of key factors to maintain the signal quality. Theinterconnections on the wiring substrate 34 suppress the degradation ofthe signal quality due to not only the impedance mismatching butelongated bonding wires.

The transmitter optical module 10 of the embodiment further provides anarrangement to suppress the degradation of the signal; that is, the toplevel of the wiring substrate 34, that of the first ceramic layer 18where the interconnections from the pads 18 b are formed, and that ofthe driver 33 are substantially leveled; which further shortens a lengthof the bonding wire.

In a transmitter optical module applied to the wavelength divisionmultiplexing (WDM) system, the precise control of an operatingtemperature of an LD is inevitable because an LD inherently shows largetemperature dependence of performances thereof. For instance, theemission wavelength, the emission efficiency, and so on strongly dependon an operating temperature. The transmitter optical module 10 of thepresent embodiment installs a TEC with a large size to control atemperature of not only the LDs 32 but the driver 33, and the opticalmultiplexer 39. The TEC 21 is mounted on the bottom 11 a of the bodyportion 11.

The first and second carriers, 30 and 35, of the embodiment are disposedon the top plate 22 of the TEC 21 in front and rear of the body portion11. Although the LDs 32 is mounted on respective LD sub-mounts 31 in thepresent embodiment, the LD sub-mounts 31 may be integrally formed in asingle body. The first carrier 30, or the LD sub-mount 31, mounts atemperature sensor to detect the temperature of the LDs 32, or that ofthe driver 33 to set the temperature of the devices, 32 or 33, in apreset condition.

The driver 33 integrates a plurality of LD drivers each drivingrespective LDs 32 independently. The driver 33 may also integrate anautomatic power control (APC) circuit to keep an average output power ofthe LD 32 in constant by feeding the output of the monitor PD 33 back tothe APC circuit. The driver 33 may integrate four (4) APC circuits eachoperating for respective LDs 32. The LDs 32 receive driving signals fromthe driver 33 via bonding wires 50.

The second carrier 35 mounts optical components, namely, the firstlenses 36, the monitor PDs 38, the optical multiplexer 39 and the secondlens 40. The first lenses 36 are placed in front of the respective LDs32 in an arrayed arrangement to concentrate light beams emitted from therespective LDs 32. The concentrated beams enter the beam splitter 37 onwhich the monitor PDs 38 are mounted. The beam splitter 37 transmits aportion of the concentrated beams, the primary portion thereof, towardthe optical multiplexer 39; while, reflects a rest portion of theconcentrated beams toward the monitor PDs 38. The rest portion of thebeam is 1 to 10% of the concentrated beam. The monitor PDs 38, which aremounted on the beam splitter 37, receive thus divided rest portion ofthe concentrated beams, and generate photocurrents. The photocurrentsare fed back to the APC circuits so as to maintain the output power ofrespective LDs 32 in constant.

Next, the arrangements around the TEC 21 will be described in detail.The TEC 21 includes a top plate 22, a bottom plate 23, and a pluralityof Peltier elements 24 provided between two plates, 22 and 23. Thebottom plate 23 faces and comes in physical contact with the bottom 11 aof the body portion 11, while, the top surface 25 of the top plate 22mounts optical and electrical components thereon through carriers, 30and 35. The top plate 22 extends rearward to just in front of the firstceramic layer 15 in the electrical plug 14. Moreover, the level of thetop surface 25 is set between the top surface 18 of first ceramic layer15 and the top surface 45 of the fourth ceramic layer 44.

The bottom plate 23 of the TEC 22 slips under the first and fourthceramic layers, 15 and 44, in the rear end thereof. A portion of thebottom plate 23 not covered by the top plate 22 provides posts 26arranged in side by side with respect to the longitudinal direction ofthe body portion 11. The posts 26 have a rectangular cross section inthe present embodiment, but, a pillared shape with a circular crosssection is applicable. The posts 26 in a top thereof are electricallyconnected to the pads in the top surface 45 of the fourth ceramic layer44.

FIG. 4 is a perspective view of the TEC 21 set within the body portion11; FIG. 5 is a plan view; and FIG. 6 magnifies a rear end of the bodyportion 11 to show an arrangement around the TEC 21. Referring to FIG.6, the electrical plug 14 includes first to fourth ceramic layers, 15 to17 and 44, where the fourth ceramic layer 44 is the lowermost layer,while, the third ceramic layer 17 is the topmost layer in the presentembodiment. Although the embodiment provides four ceramic layers, thebody portion 11 may be formed by five or more ceramic layers.

The first ceramic layer 15 extends externally and internally to form aterrace where the external pads 18 b, internal pads, andinterconnections electrically connecting them are provided. The lattertwo elements, namely, the internal pads and the interconnections are notexplicitly illustrated in the figure. The inner edge 18 c of the topsurface 18 in respective sides thereof is back off to expose the topsurface 45 of the fourth ceramic layer 44 to form exposed areas 45 a and45 b of the lowermost layers 44.

The second ceramic layer 16, which is put on the first ceramic layer 15,provides a top surface 19 exposed inside of the body portion 11. The topsurface 19 in a front edge thereof is back off to expose the top surface18 of the first ceramic layer 15. The top surface 19 of the secondceramic layer also forms interconnection electrically connected to thedriver 33. Because the top surface 19 is not extended outside of thebody portion 11, via holes piercing the second ceramic layer 16electrically connect the interconnections on the top surface 19 to thoseformed on the top surface 18 of the first ceramic layer 15. Thus, theinterconnections provided on the top surface 19 are preferably providedfor signals containing lower frequencies.

The third ceramic layer 17, which is put on the second ceramic layer 16,is configured to be a wall to form a cavity within the body portion 11.The third ceramic layer 17 exposes the top surface 19 of the secondceramic layer 16. While, the fourth ceramic layer 44 is provided underthe first ceramic layer 15 and provides the top surface 45 exposedwithin the inside of the body portion 11 and respective sides thereof.

The top surface 45 provides an electrical pads 46 on the exposed areas45 a and 45 b. Because the top surface 45 of the fourth ceramic layer 44is exposed only in respective sides of the body portion 11 to form theexposed areas 45 a and 45 b of the top surface 45, the bottom plate 23of the TEC 21 may be extended between the exposed areas 45 a and 45 b ofthe top surface 45. That is, the rear end of the bottom plate 23 is setin a cut between the exposed areas 45 a and 45 b of the top surface 45.Moreover, the rear portion of the bottom plate 23 provides the posts 26to supply a current to the TEC 21. Accordingly, the posts 26 on thebottom plate 23 and the electrical pads 46 on the top surface 45 arearranged in side-by-side. Connecting the electrical pad 46 to the post26 with bonding wires 48, the current to drive the TEC 21 is supplied.This arrangement of two electrodes, 26 and 46, are suitable for drawinga plurality of bonding wires 48 with a shorter length. Moreover, theside-by-side arrangement of the electrodes may be formed only bystacking the ceramic layers, 44 and 15, without cutting, processing, andso on of the ceramic material.

The electrical pad 46 is connected to the pad 18 b prepared in the plug14 by a via hole piercing the first ceramic layer 15. When theelectrical pad 46 is connected to another pad formed in the back surfaceof the first ceramic layer 15, which is not illustrated in the figures,the electrical pad 46 is directly connected to those pads withoutpassing any via holes. As shown in the figures, the bonding wires 48connecting two pads 46 with the posts 26, extend laterally of the bodyportion 11 and with a relatively shorter length.

FIG. 7 shows a side cross section of the TEC 21 showing a positionalrelation of the TEC 21, the first and fourth ceramic layers, 15 and 44,and the bonding wires 48. As shown in FIG. 7, the bonding wires 48 in atop level thereof is lowered from the top surface 25 of the TEC 21.Accordingly, the top surface 45 of the fourth ceramic layer 44 and thetop of the post 26 are set in a level lowered from the top surface 25 ofthe TEC 21. Accordingly, even when the first carrier 30 extrudes fromthe edge of the top plate 22 of the TEC 21 rearward, the first carrier30 does not interfere with the bonding wires 48.

As shown in FIG. 3, the wiring substrate 34 also protrudes rearward fromthe edge of the first carrier 30 so as to set the rear edge of thewiring substrate 34 further close to the front edge of the first ceramiclayer 15. This arrangement enables to connect the interconnection on thetop surface 18 of the first ceramic layer 15 with the interconnection onthe wiring substrate with a shorter bonding wire. Because the positionof the LDs 32 measured from the front wall of the body portion isoptically determined, and the driver 33 has definite planar dimensions,the rear edge of the driver 33 is sometimes apart from the front edge ofthe first ceramic layer 15, which probably results in a lengthenedbonding wires between the driver 33 and the first ceramic layer 15. Thewiring substrate 34 with an optional length may compensate such alengthened bonding wire. Shortened bonding wire may suppress degradationof the signal quality in high frequencies.

In another situation, when a pitch between the electrodes on the topsurface 18 of the first ceramic layer 15 is far different form a pitchbetween the pads formed on the driver 33, the wiring substrate 34 isprovided for a device to convert the pitches. The driver 33 is anintegrated circuit (IC) on a silicon wafer, and has a minimum die areato build the necessary circuit therein. Accordingly, the pitch betweenthe pads on the driver 33 is designed to be 100 to 200 μm at most. Onthe other hand, the electrodes provided in the electrical plug 14 oftenhave the pitch of at least 200 to 400 μm. Moreover, when an opticalmodule has plural channels operating over 10 Gbps and the pads withinthe driver 33 has the pitch different from the pitch of the electrodes;a time lag becomes large between signals carried on the outermostinterconnection and those on the inner interconnection. The wiringsubstrate 34 adequately compensates the time lag by drawinginterconnection on the substrate 34 such that the inner interconnectionhas a length substantially equal to a length of the outerinterconnection.

The arrangement of the TEC 21, the post 26, and the electrical pad 46 ofthe fourth ceramic layer 44 make the electrical plug 14 to be formedonly in the rear end of the body portion 11. Thus, the transmitteroptical module with a slimed width may be easily available. Such amodule, even when the module installs a plurality of optical sources torealize a total transmission speed of 40 Gbps and/or 100 Gbps, may beinstalled within a newly proposed transceivers type of CFP2, CFP4, andso on having an optical connector of the LC type.

FIGS. 8 and 9 show another embodiment, where the transmitter opticalmodule shown in FIGS. 8 and 9 removes the wiring substrate 34 providedon the first carrier 30 and electrically connecting the interconnectionon the first ceramic layer 15 to the driver 33A. When the pads formedwithin the driver 33A have a relatively wider pitch substantially equalto the pitch of the electrodes 18 b on the first ceramic layer 18,because the driver 33 integrates supplemental circuit therein andresultantly the die area inevitably becomes large, the transmittermodule 10 may remove the wiring substrate 34. The embodiment shown inFIG. 9 sets the rear end of driver 33A close to the front edge of thefirst ceramic layer 15. The arrangement shown in FIGS. 8 and 9 removesthe bonding wire 50 connecting the interconnection provided on thewiring substrate 34 and the driver 33A, which suppresses the degradationdue to the existence of this bonding wire.

In the foregoing detailed description, the transmitter optical module ofthe present invention have been described with reference to specificexemplary embodiments thereof. It will, however, be evident that variousmodifications and changes may be made thereto without departing from thebroader spirit and scope of the present invention. The presentspecification and figures are accordingly to be regarded as illustrativerather than restrictive.

What is claimed is:
 1. A transmitter optical module, comprising: asemiconductor laser diode (LD) to emit light with a specific wavelength;a thermo-electric-controller (TEC) to control a temperature of the (LD),the TEC including a bottom plate and a post provided on the bottomplate; and a body portion configured to enclose the LD and the TECtherein hermetically, the body portion including an electrical plug madeof multi-layered ceramics including a lowermost layer providing anelectrical pad on a top surface thereof exposed within the body portion,the electrical pad supplying a current to the TEC through the post,wherein the post and the electrical pad are configured in side-by-sidearrangement and electrically connected with a bonding wire, wherein themulti-layered ceramics of the electrical plug further includes a firstceramic layer providing an interconnection electrically connecting aninside of the body portion to an outside thereof, the interconnection ofthe first layer providing an electrical pad in an end outside of thebody portion.
 2. The transmitter optical module of claim 1, wherein thebottom plate of the TEC is slipped under the lowermost layer of themulti-layered ceramics of the electrical plug.
 3. The transmitteroptical module of claim 1, wherein the post on the bottom plate of theTEC has a level lower than a level of the top surface of the lowermostlayer exposed within the body portion.
 4. The transmitter optical moduleof claim 1, wherein the first ceramic layer provides interconnections ina top surface and a back surface thereof, the electric pad on the topsurface of the lowermost ceramic layer exposed within the body portionbeing electrically connected to the interconnection in the back surfaceof the first ceramic layer.
 5. The transmitter optical module of claim1, wherein the bonding wire has a top level lower than a top level ofthe TEC.
 6. A transmitter optical module, comprising: a plurality oflaser diodes (LDs) each emitting light having wavelengths different fromeach other; a thermo-electric-controller (TEC) to control a temperatureof the LDs, the TEC including a bottom plate and a post provided on thebottom plate; a body portion configured to enclose the LDs and the TECtherein hermetically, the body portion including an electrical plug madeof multi-layered ceramics including an electrical pad that supplies acurrent to the TEC through the post, the electrical pad being arrangedside-by-side with respect to the post of the TEC; a driver for drivingthe LDs electrically; and an optical multiplexer that multiplexes thelight emitted from the LDs, wherein the LDs and the driver are installedon the IBC through a first carrier, and the optical multiplexer isinstalled on the TEC through a second carrier different from the firstcarrier.
 7. The transmitter optical module of claim 6, further includinga wiring substrate provided on the first carrier, the wiring substrateproviding an interconnection electrically connected to the driver. 8.The transmitter optical module of claim 7, wherein the wiring substrateextends outwardly from an edge of the first carrier to the electricalplug.
 9. The transmitter optical module of claim 6, wherein the TECprovides a top plate, the first carrier extending outwardly from an edgeof a top plate of the TEC toward the plug.
 10. The transmitter opticalmodule of claim 6, wherein the multi-layered ceramics of the electricalplug includes a lowermost layer and a first ceramic layer on thelowermost layer, the electrical pad being provided on a top surface of aportion of the lowermost layer exposed from the first ceramic layer, andwherein the first ceramic layer provides an interconnection electricallyconnecting an inside of the body portion to an outside thereof, theinterconnection of the first ceramic layer providing an electrical padin an end outside of the body portion.
 11. The transmitter opticalmodule of claim 10, wherein the first ceramic layer forms exposed areasin respective sides of the lowermost layer by exposing the top surfaceof the lowermost ceramic layer, and wherein the post provided on thebottom plate of the TEC is put between the exposed areas in therespective sides of the top surface of the lowermost ceramic layerexposed by the first ceramic layer.
 12. The transmitter optical moduleof claim 6, wherein the bonding wire has a top level lower than a toplevel of the TEC.
 13. A transmitter optical module, comprising: asemiconductor laser diode (LD) configured to emit light with a specificwavelength; a thermo-electric-controller (TEC) configured to control atemperature of the LD, the TEC including a bottom plate and a postprovided on the bottom plate thereof; a body portion configured toenclose the LD and the TEC therein hermetically, the body portionincluding an electrical plug made of multi-layered ceramics including anelectrical pad that supplies a current to the TEC through the post; anda coupling portion assembled with one side of the body portion oppositeto a side where the electrical plug is formed, wherein the post and thepad are configured in side-by-side arrangement and electricallyconnected with a bonding wire, and wherein the body portion provides noelectrical structures in both sides connecting the side where thecoupling portion is assembled to the side where the electrical plug isformed.